Mellouli, N.; Nibirantiza, A.; Radoux, F.
(Symmetry, Integrability and Geometry: Methods and Applications, 2013)
We consider the space of differential operators Dλμ acting between λ- and μ-densities defined on S¹|² endowed with its standard contact structure. This contact structure allows one to define a filtration on Dλμ which is ...